Head in the air

Frank Stratmann studies clouds in every shape and form. He chases after them in the open sky and breeds them in a lab to discover the mysteries of the ­phenomena that float almost daily above us.

Frank Stratmann is always happy to see clouds because, as a nephologist (cloud researcher), he studies them. When the sky darkens or becomes overcast, he pays particular attention. Gray giants are his favorite: “Storm clouds are amazing,” he says, because they are so packed with energy. Stratmann always see a litte bit more in clouds than other people do.

Studying clouds is quite a challenge in itself. They are hard to reach, fleeting, constantly moving. They arise, flow together, separate again. You cannot simply pluck them from the sky and clamp them under a microscope. And plus, every cloud is different. Nevertheless, Stratmann wants to make them calculable, to express their fluffy formations in figures and formulas. Before he can do that, he still has several puzzles to solve. How are clouds formed? What role do dust particles in the air play, and how does wind influence clouds?

The sky over Leipzig is as clear and blue as a swimming pool. No white streaks or spots, not a cloud to be seen far and wide. Still, Stratmann has enough work to do because he and his team make their own clouds at the Leibniz Institute for Tropospheric Research, the only one of its kind in the world. The lab is part of a science park on the edge of town and easily spotted from a distance thanks to its 16-meter-high tower. The clouds grow in a wind tunnel that extends over four stories. The lab buzzes like a cold store and everywhere there are pipes and cables, metal rails, gray devices with flashing numbers, and open laptops – so much technology just to imitate Nature.

Yet the recipe for a cloud is incredibly simple: You need damp air, wind and a handful of tiny floating particles, or aerosols. On the second level of the cloud tower, Stratmann prepares the particles in a clear solution, which he atomizes in the wind tunnel. Pollen, sea salt, desert sand – these particles are found floating around in the air everywhere outside. Without them, there would be no clouds. It’s in contact with particles that damp air condenses in the atmosphere, so that little droplets form and begin growing into a cloud. Breathe out into the icy air on a cold winter’s day and you can see it: Your warm breath turns into fog, and a cloud is born. That’s exactly what happens inside the simulator, too. Green laser lights render the white swathes visible inside the dark wind tunnel. They descend like a waterfall. The sky here in the lab is not only bright green, it’s also upside down. “The clouds float so nicely and fluffily in the sky, but they are tremendously complicated,” says Stratmann, who talks passionately about buoyancy, relative humidity and ice nucleation.

These are just some of the terms he uses to describe vital events taking place in the sky. A brief refresher: Without clouds, the earth would be a barren place in many parts. Clouds store the water that evaporates from lakes, rivers and oceans, carry it away and distribute it in the form of rain. Even when they look light as feathers, clouds may be incredibly heavy. They consist of millions of minute droplets. A regular fine-weather cloud one square kilometer in area can contain roughly 200 tons of ­water, a thundercloud, as much as hundreds of thousands of tons. When the drops become too large and heavy, they fall as rain.

The English apothecary Luke Howard (1772-1864), who is generally considered to be the world’s first nephologist, had no clue about the details of clouds, but he determined types among the many and diverse forms and gave them the Latin names they bear today: cumulus, cirrus, stratus. Continuous refinements and additions have since been made to their classification, and it was only in 2017, 30 years since publishing the last one, that the World Meteorological Organization (WMO) came out with a new cloud atlas defining the following supplementary features: cauda, or tail cloud, because it resembles the tail of a comet; and asperitas which seen from below, resembles rippling waves.

Leipzig landmark: The 16-meter wind tunnel tower at the Institute for Tropospheric is the only one of its kind in the world

Stratmann cannot work with such unusual shapes. He likes what he studies to be as regularly formed as possible. In the lab, he can regulate conditions precisely so that the ungraspable can be experienced and understood. He varies the particles, humidity, temperature and wind speed – and observes the result. Numbers and curves on computer screens reveal the clouds’ characteristics. Clouds are the great unknown factor in climate computations, capable of slowing or accelerating climate change. “Clouds can heat or cool,” Stratmann explains. Some reflect the sun’s rays back into space. Others capture the heat and envelope the earth like a wooly comforter.

Nowadays, scientists send measuring instruments skywards or climb mountains, analyze satellite images, and use lasers and radar to measure clouds from the ground. Science is, however, still far from having discovered any generally applicable cloud formulas, Stratmann admits. Lufthansa aircraft also gather samples and data, which are then used by the people at the institute. As part of the Caribic project, passenger aircraft are regularly equipped with high-tech measuring apparatus for atmospheric observation. Flying laboratories on scheduled flights, they also take readings from clouds ten kilometers above the earth. Stratmann occasionally goes up in a helicopter himself, but not into every cloud. “If the pilot says no, you have to accept it,” he says. Unfortunately, it’s often precisely those clouds that he’s most interested in – ice clouds, for instance, at the moment they freeze. But Stratmann takes this in his stride and, back at the lab, simply makes his own.